This invention relates to vehicle engine valves, and in particular to a scraping and filtering device for reducing contaminant build-up on a valve shaft.
It is known in the art relating to vehicle engine valves that some valve designs are particularly susceptible to contaminant built-up on the valve shaft. One such design is the exhaust gas recirculation (EGR) valve, which selectively adds a partial flow of exhaust gas into the intake manifold of a vehicle to mix with fresh intake air to lower the combustion temperature thereby decreasing exhaust emissions.
EGR valves generally include a valve assembly, connected with a solenoid actuator assembly, operable to close or open a passage between the intake and exhaust manifolds. The valve assembly includes a valve member including a valve shaft supported by a bearing for reciprocating motion along a central axis on which a valve body is aligned.
EGR valves are designed so that the clearance between the shaft and the bearing is as small as practicable without interfering significantly with valve actuation so as to minimize leakage of exhaust gas. However, the need to minimize gas leakage is balanced against the need to minimize hysteresis (and thus enhance actuator performance) which requires the diametral clearance between the valve shaft and its supporting bearing to be as large as possible (i.e. large enough to permit only an acceptable amount of exhaust gas leakage, less than 0.5 g/s, while limiting moisture intrusion).
In operation, the valve shaft is selectively exposed to exhaust gas as it operates to selectively admit exhaust gas into the valve assembly. Because exhaust gas (particularly diesel exhaust gas) has a high moisture content and is laden with particulates, the valve shaft may become coked, and the coking drawn into the bearing when the valve is closed. The accumulation of contaminants on the surfaces of the valve shaft and bearing may ultimately cause the shaft to seize in the bearing. It is therefore desirable to provide a simple, cost-effective means for removing contaminant build-up on a valve shaft.
Additionally, some engine designs are impractical to completely rid of debris prior to assembly. In such cases, loose debris can lodge between the valve shaft and its bearing rendering the valve inoperable. It is therefore desirable to provide a means for filtering or collecting loose debris where engine cleanliness prior to assembly is problematic.
The present invention provides a valve shaft scraper and filter for cleaning the shaft of a valve assembly to prevent coking and failure of the valve. The valve shaft scraper and filter is an annulus of woven metal mesh disposed within a cavity in the valve assembly to surround the valve shaft. As the valve shaft reciprocates through the valve assembly, it passes through the annulus which gently scrapes against the outer surface of the valve shaft to remove contaminant build-up on the shaft. To this end, the annulus has the closest diametral relationship possible with the valve shaft while enjoying a limited range of axial and radial movement within the cavity so as neither to compromise operation of the actuator on the shaft nor impart hysteresis on the shaft.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.